1. Field of the Invention
The present invention is related to a device which compresses color still image data, for example, in accordance with a JPEG (Joint Photographic Expert Group) algorithm and records the compressed image data in a recording medium and, also, to a device which reads the compressed image data from the recording medium and expands the compressed image data to reproduce the color still image.
2. Description of the Related Art
A standard algorithm, for the encoding of high resolution images and the transfer of that information through telecommunication transmission channels, has been recommended by the JPEG. In order to enable a large-scale data compression, the baseline process of the JPEG algorithm breaks down the original image data into components on a spatial frequency axis using a two-dimensional DCT process. Thereafter, the data expressed on the spatial frequency axis is quantized by using a quantization table. The quantized data is then encoded using a Huffman table.
There is known a so-called pixel offset method, in which, for example, one color still image is color-separated into red, green and blue images. These three images are then offset with respect to each other, by, for example, one-third of one pixel in a horizontal direction, as they are formed on an imaging device. According to the pixel offset method, a high definition image can be obtained, because the pixel data are now obtained for every one-third of a pixel.
In a conventional device, when compressing the image data, which are obtained by using the pixel offset method, according to the JPEG, as a pre-stage of the image process, a high definition image is initially generated using all of the color pixel data obtained by the pixel offset method, and then, a compression process is carried out on the high definition image. Therefore, the time it takes to record the compressed image data in a recording medium is extended, and the amount of the compressed data is large.